1. Field of the Invention
The present invention relates to paper machine fabrics, and particularly but not exclusively to forming fabrics for use in the forming section of a papermaking machine.
2. Discussion of Background Information
Paper is conventionally manufactured by conveying a paper furnish, usually consisting of an initial slurry of cellulosic fibers, on a forming fabric or between two forming fabrics in a forming section, the nascent sheet then being passed through a pressing section and ultimately through a drying section of a papermaking machine. In the case of standard tissue paper machines, the paper web is transferred from the press fabric to a Yankee dryer cylinder and then creped.
Paper machine clothing is essentially employed to carry the paper web through these various stages of the papermaking machine. In the forming section the fibrous furnish is wet-laid onto a moving forming wire and water drainage from it is assisted by means of suction boxes and foils. The paper web is then transferred to a press fabric that conveys it through the pressing section, where it usually passes through a series of pressure nips formed by rotating cylindrical press rolls. Water is squeezed from the paper web and into the press fabric as the web and fabric pass through the nip together. In the final stage, the paper web is transferred either to a Yankee dryer, in the case of tissue paper manufacture, or to a set of dryer cylinders upon which, aided by the clamping action of the dryer fabric, the majority of the remaining water is evaporated.
So called “triple layer” paper machine fabrics are known in the art. These generally comprise paper side and machine side warp and weft yarn systems, which are bound together by binder yarns.
EP 1,000,197A and EP 1,158,090A both disclose triple layer fabric in which the paper side weave is obtained by the interweaving of paper side machine direction (MD) or warp yarns with both individual, non-interchanging, paper side weft yarns and interchanging pairs of weft yarns which, in addition to forming part of the paper side weave, also act to bind the paper side and 5 wear side fabrics together.
While structures made according to EP 1,000,197A and EP 1,158,090A have given good performance, in some respects, they have been found to be rather high in thickness such that water carried within the fabric void space may, near the end of the paper machine's sheet forming section, rewet the paper sheet resulting in decreased machine efficiency. EP 1,273,698A seeks to resolve this issue by incorporating thinner MD and CD (cross machine direction) yarns such that thinner fabrics containing less void space are provided. While this approach is helpful in resolving the so-called “sheet rewet” issue it creates a new problem in that the finer fabric has reduced CD bending stiffness and consequently the less stable fabric has a decreased ability to minimize sheet basis weight profiles.
The present invention has been made from a consideration of these problems.